1. Field of the Invention
The present invention relates to a tilt angle adjusting device and a projector equipped with the tilt angle adjusting device. More particularly, the present invention relates to a device for adjusting the orientation of a projector.
2. Description of the Related Art
A typical projector is equipped with a tilt angle adjusting device to adjust a longitudinal and a transverse inclination of the projector in accordance with various situations. Conventional tilt angle adjusting devices are generally classified into two types according to the tilt angle adjusting mechanism. In a tilt angle adjusting device of the first type, extending lengths of tilt feet arranged on the bottom of a housing are varied in order to incline the housing in a longitudinal and/or transverse direction. In a tilt angle adjusting device of the second type, a housing is tiltably mounted on a pedestal and tilted on the pedestal in order to incline the housing in a longitudinal and/or transverse direction.
Irrespective of which type of tilt angle adjusting device is used, a change in the longitudinal inclination of projector 100 causes a change in the projected angle of the centerline of image light in the vertical direction (referred to as a projection angle hereinafter), so that a displayed position of image 101 is moved up and down, as illustrated in FIG. 1. On the other hand, a change in the transverse inclination of projector 100 causes a change in the projected angle of the centerline of image light in the horizontal direction (referred to as an image angle hereinafter), so that image 101 is displayed such that the upper right or the upper left portion of the image is raised, as illustrated in FIG. 2.
FIGS. 3A to 3D illustrate examples of projectors which are equipped with a tilt angle adjusting device according to the first type. Projectors 102 of FIGS. 3A to 3D are commonly equipped with at least one tilt foot 105 on bottom surface 104 of housing 103. In projector 102 illustrated in FIG. 3A, one tilt foot 105 is arranged in the front portion of bottom surface 104, and two fixed legs 106 are arranged in the rear portion of bottom surface 104. The term “fixed leg” used herein refers to a leg, the length of which cannot be adjusted, unlike tilt foot 105. In projector 102 illustrated in FIG. 3B, one tilt foot 105 is arranged in the front portion of bottom surface 104, and one tilt foot 105 and one fixed leg 106 are arranged in the rear portion of bottom surface 104. In projector 102 illustrated in FIG. 3C, two tilt feet 105 are arranged in the front portion of bottom surface 104, and one fixed leg 106 is arranged in the rear portion of bottom surface 104. In projector 102 illustrated in FIG. 3D, two tilt feet 105 are arranged in the front portion of bottom surface 104, and two fixed legs 106 are arranged in the rear portion of bottom surface 104.
In projector 102 illustrated in FIG. 3A, tilt foot 105 can be lengthened or shortened to adjust the projection angle. In projector 102 illustrated in FIG. 3B, front and rear tilt feet 105 can be lengthened or shortened to adjust the projection angle and the image angle independently of each other. In projectors 102 illustrated in FIGS. 3C, 3D, two front tilt feet 105 can be lengthened or shortened to adjust both the projection angle and the image angle at one time.
Another example of the first type of a tilt angle adjusting device is described in the specification etc. of Japanese Patent Laid-open Publication No. 2001-42423 (Document 1). The tilt angle adjusting device described herein comprises a support leg pivotally arranged on the bottom surface of a housing of a projector; and a fixing mechanism for fixing the support leg at a desired angle. The fixing mechanism comprises an operating gear which rotates in association with pivotal movements of the support leg, and a rotating gear fixed to the housing. The operating gear usually meshes with the rotating gear. The operating gear, however, is released from engagement with the rotating gear when it slides in the horizontal direction. Specifically, as a release button is pushed, the operating gear slides in the horizontal direction away from the rotating gear to allow the operating gear to be released from engagement with the rotating gear, and to allow pivotal movement of the support leg. As the release button is released after the support leg has been pivotally moved to a desired angle, the operating gear slides in the opposite direction and comes into mesh with the rotating gear to lock the support leg.
The specification etc. of Japanese Patent Laid-open Publication No. 2004-109359 (Document 2) describes a projector which has a tilt angle adjusting device of the second type. The projector described herein is provided with a hemispherical protrusion on the bottom surface of the housing of the projector. A pedestal on which the projector is mounted has a top surface provided with a hole into which the protrusion is fitted. Thus, as the projector is placed on the pedestal such that the protrusion is fitted into the hole, the projector can be inclined to the front, back, right, and left on the pedestal, as well as rotated in the horizontal direction.
Although the tilt angle adjusting device illustrated in FIG. 3A can adjust the projection angle, it cannot adjust the image angle, and although the tilt angle adjusting device illustrated in FIG. 3B can adjust both the projection angle and image angle, it cannot adjust them at one time. Therefore, either the projection angle or the image angle must be adjusted first, then followed by the adjustment of the other. Although the tilt angle adjusting mechanisms illustrated in FIGS. 3C, 3D can adjust the projection angle and image angle at one time, they cannot adjust them independently of each other (i.e., individually). Further, to adjust the angles, any of the tilt angle adjusting devices illustrated in FIGS. 3A-3D must be lifted up to raise the tilt foot (feet), resulting in complicated and burdensome adjustment work.
The projector described in Document 1 involves complicated and burdensome work for adjustments, because the release button must be pushed each time the angle is adjusted. Further, the housing must be lifted up to raise the support leg to adjust the angle, similar to the tilt angle adjusting devices illustrated in FIGS. 3A-3D.
In the projector described in Document 2, the orientation of the housing is only maintained by the frictional resistance of the surface of the protrusion with the periphery of the hole. As such, the orientation can vary with only small force applied to the housing. Further, if the housing is inclined at an excessive angle, the frictional resistance of the surface of the protrusion with the periphery of the hole may not be sufficient to maintain the orientation of the housing. Even if the orientation is maintained, the orientation of the housing is liable to vary with any slight force.